Double hung window assemblies generally include a window frame, a lower window sash, an upper window sash, a pair of window jambs, two sets of jamb pockets, and at least one window balance device for offsetting the weight of a window sash throughout a range of travel within the window frame. A typical block and tackle window balance device uses a combination of a spring and pulleys located within a channel to balance the weight of the window sash at any position within the window jamb. In some block and tackle window balance devices, the channel containing both the spring and pulleys is attached to the window sash. The device includes a cord that passes through the pulley system and is attached to a jamb mounting hook that is connected to a side jamb.
In general, block and tackle window balance devices often incorporate springs capable of storing a substantial amount of potential energy when the springs are loaded in tension. Typically, a cord or chain is used to provide tension to the spring. Should the cord or chain break or become detached from the mounting hook, the sudden spring retraction may result in the spring mechanism becoming detached and could result in damage to the sash.
There exist several configurations of block and tackle window balance devices containing both springs and pulleys. See, for example, U.S. Pat. No. 5,737,877 issued to Meunier et al., the disclosure of which is hereby incorporated herein by reference in its entirety. Meunier discloses the use of a block and tackle balance disposed between a jambliner and a window sash. See also, for example, U.S. patent application Ser. No. 09/810,868 entitled “Block and Tackle Window Balance with Bottom Guide Roller” by Newman, the disclosure of which is also hereby incorporated herein by reference in its entirety. Newman discloses a block and tackle window balance device that provides an increased range of sash travel within a window frame.
Some window balance systems provide a manually-activated brake that can be set, for example, using a wrench, to inhibit the release of stored potential energy in a block and tackle window balance. Such manually operated brakes are user activated, for example, during an installation and/or removal procedure of the balance device. Unfortunately, manually-activated brakes will not protect against an unintentional release of stored potential energy. Further, an unskilled user may not be aware that the manually-activated brake system is available, as the brake actuator is typically located on the balance device, behind a jamb plate. Thus, it is generally hidden from view, only being observable through a small hole or narrow slit in the jamb.